Individuals exposed to fear-evoking stressors are at increased risk for a number of psychiatric illnesses including post-traumatic stress disorder, major depressive disorder, and generalized anxiety disorder. These debilitating conditions are among the most significant public health problems facing the United States today. Understanding the central neuropharmacological and molecular mechanisms that drive responses to fear- evoking stressors will enable us to identify points of dysregulation that may contribute to development of stress-related disorders and also identify targets for the development of effective treatment options. The bed nucleus of the stria terminalis, which has recently emerged as an important component of stress regulation circuitry, contains dense terminals that release the neuropeptide calcitonin gene-related peptide (CGRP). Very recently, behavioral evidence has implicated CGRP signaling within the BNST in anxiety and also points to the possibility that BNST CGRP may modulate behavioral and neuroendocrine responses to stress. The first goal of this present research, then, is to test the hypothesis that CGRP signaling within the BNST enhances anxiety-like behavioral and hypothalamic-pituitary-adrenal (HPA) axis responses to stress. I will manipulate BNST CGRP signaling using 1) infusion of a CGRP antagonist, 1CGRP8-37 into the BNST via intracranial cannulae and 2) BNST CGRP receptor sensitization by lentiviral-mediated over-expression of RAMP1, the CGRP receptor subunit that confers pharmacological specificity for CGRP and influences glycosylation and trafficking of the CGRP receptor to the cell surface. Following manipulation of BNST signaling, rats will be exposed to a fear-evoking stressor (trimethlythiazoline odor). We will measure fear- and anxiety-like behavior (acoustic startle and defensive freezing), neuroendocrine responses (serum corticosterone and adrenocorticotropin hormone), and changes in mRNA expression of CGRP, and the CGRP receptor components RAMP1 and calcitonin receptor-like receptor (CRLR). Also, because CGRP terminals within the BNST form perisomatic baskets around neurons containing the stress-related neuropeptide corticotropin- releasing factor (CRF), another goal of this research is to determine if CGRP signaling affects activation of BNST CRF-containing neurons to influence anxiety behavior and HPA axis activity. In order to test the hypothesis that BNST CGRP enhances BNST CRF neuron activation to increase CRFr1 receptor signaling in stress-related target structures, rats will be treated with a systemic CRFr1 antagonist (GSK876008) or infected with lentiviral-mediated CRF siRNA to knock down CRF expression within the BNST and then they will be infused with intra-BNST CGRP and tested as described above. The results of these studies could provide the first pieces of evidence to demonstrate BNST CGRP modulation of behavioral and neuroendocrine stress responses and influence on stress-related neurotransmitter signaling pathways. This research may also present a novel therapeutic target in the treatment of stress-related psychiatric disorders. PUBLIC HEALTH RELEVANCE: Individuals exposed to fear-evoking stressors are at increased risk for a number of psychiatric illnesses including post-traumatic stress disorder, major depressive disorder, and generalized anxiety disorder. The bed nucleus of the stria terminalis (BNST), which contains numerous calcitonin gene-related peptide (CGRP) immunopositive terminals, has recently been identified as a pivotal relay of cortical information to neural structures mediating behavioral and neuroendocrine responses to stress. The proposed research will investigate the role of CGRP signaling within the BNST in fear- and anxiety-like behavioral and neuroendocrine stress responses, and may present a novel therapeutic target in the treatment of stress-related psychopathologies.